I really believe Plowman is still a walk-up start in the best 22. Haven't been a huge fan of him for a while now but there is nobody else on our list to play that roll in the team. Playing Kemp in that role seems to be a waste of his skill and talent, and Boyd is just not big enough imo.
I believe Plowman was coming back from an injury when he played in the VFL game instead of being named for the AAMI game, so I think it may have been him easing back into it, rather than actually being dropped from the best 22.
That being said, it is still strange to me that he played the last quarter in the AAMI game if he was coming back from injury.
As for Kemp, he will likely be in and out of the team a fair bit this year. Its a blessing and a curse with his versatility - hopefully he picks a position and sticks with it soon.